1. Field of the Invention
The present invention relates to a legged robot capable of running. It should be noted that a legged robot may be simply referred to as “robot” hereinafter.
2. Description of the Prior Art
Legged robots which can move by driving the joints disposed in the legs are being developed. The number of the legs may vary in robots. A biped robot moves like a human, and a quadruped robot moves like an animal. A monoped robot moves while hopping.
Humans and animals present a behavior of “running” rather than “walking” for a fast travel. It is also preferable for legged robots being able to perform the behavior of “running” for a fast travel. “Walking” is a movement in which at least one of the legs is in contact with the ground; whereas “running” is a movement that a state in which at least one of the legs is in contact with the ground and a state in which all the legs are off the ground are repeated periodically. The state in which one of the legs is in contact with the ground which lasts during a period from the landing to the takeoff of that leg, is hereinafter referred to as “ground-contact phase”. More specifically, the “ground-contact (ground-contact timing)” is a timing at which the state of all the legs being off the ground transitions to the state of having one of the legs touching the ground. “Takeoff (takeoff timing)” is a timing at which the state of having one of the legs in contact with the ground transitions to the state of having all the legs taken off the ground. The state in which all the legs are off the ground is during a period from the takeoff to the landing, which is hereinafter referred to as “aerial phase”. One periodic cycle constituted by the ground-contact phase and the aerial phase is referred to as “jump cycle”. A motion of a robot across one jump cycle is referred to as a “jump motion”. Thus, “running” herein means moving while repeating the jump cycle constituted by the ground-contact phase and the aerial phase. The motion of the legged robot having one leg and that moves while hopping is also referred to as “running”, in which the jump cycle is repeated. Moreover, the period from the landing to the takeoff of the leg is referred to as “ground-contact phase period”, and the period from the takeoff to the landing is referred to as “aerial phase period” hereinafter.
A legged robot which runs (jumps) is disclosed in Japanese Patent Application Publication No. 2003-80477 and in WO 2003/057429.